The present invention relates to a magnetic disk cartridge and, more particularly, to a magnetic disk cartridge in which a center core fixed to the central portion of a magnetic disk is improved.
Conventionally, there has been widely used a magnetic disk cartridge a 3.5-inch micro floppy disk in which a magnetic disk is rotatably received in a cartridge case formed of a relatively hard material.
In the conventional magnetic disk cartridge, as shown in FIG. 4, there is provided a magnetic disk 1 and a center core 2 mounted to the central portion of the magnetic disk 1. The magnetic disk 1 is rotatably received in a cartridge case (not shown). The center core 2 is formed of a metal plate (a magnetic substance) having relatively good malleability. As shown in FIG. 5 (which is an enlarged section view taken along a line A--A in FIG. 4), the center core 2 includes a flange 2c provided in the outer peripheral portion thereof and two engagement holes 2a, 2b formed by drawing. The flange 2c is used to fix the core 2 to the magnetic disk 1 by means of an adhesive member 3 such as a double-sided tape or the like. When in use, a drive shaft D is inserted into one of the two engagement holes, namely, the engagement hole 2a (a cylindrical hole having a burred edge portion), which is formed in the center of the center core 2, while a positioning pin P is inserted into the other engagement hole 2b.
The flange 2c includes an inner peripheral corner portion 2d, while the center core 2 includes a bottom outer peripheral corner portion 2e. Due to the drawing machining process used to form them, the two corner portions 2d and 2d have a certain curvature. In manufacturing the magnetic disk cartridge, prior to final assembly, the drawn center core 2 can be stored and held in various conditions; for example, a large number of center cores are often stored in a case or the like before they are delivered for assembly with magnetic discs, or the center cores are stored in a hopper or the like forming a center core supply device provided in an automatic assembly facility.
In other words, the center cores 2 are sometimes stacked on each other. In some of the stacked center cores 2, for example, as shown in FIG. 6, there occurs a condition wherein, with the centers of the center cores coincident with each other, the center cores are vertically superimposed on each other. In such a superimposed state, in the portions of the center cores 2 designed by B in FIG. 6, the inner peripheral corner portion 2d and the bottom outer peripheral corner portion 2e can bite into each other due to manufacturing tolerances in the dimensions of the cores 2. If two or more center cores 2 are delivered in such a state, the center core delivery line may be stopped or other problems occur. In such an instance, such center cores 2 must be taken away from the delivery line and detached from each other by hand, then sent back again to the delivery line. This requires extra labor and time.
In order to eliminate the above inconvenience, for example, as disclosed in Japanese Utility Model Publication No. Hei. 2-16456, a center core is employed in which the metal plate of the center core is inserted into a synthetic resin member to thereby form the flange portion of the core plate as a resin portion, and the bottom surface (chucking surface) of the center core is made larger than the inner periphery of the flange, thereby to avoid the above-mentioned biting phenomenon.
However, in the above-mentioned conventional method, in addition to the step of forming the metal plate portion of the center core, there is added a step of inserting and molding the metal plate portion into a synthetic resin member, which increases the number of manufacturing steps. As a result, the productivity of the conventional method is lowered, while the costs of the center core are increased.